In the reconditioning of automobile and other engines a frequent need is to replace or rework the valve guides and seats. The valve locations are usually arranged in a single row: at one time their axes were all normal to the machined reference surface of the block -- or of the head, in the case of valve-in-head engines. However, it is now common to find the valve axes lying in a common plane which is not normal to the reference surface. The exhaust valves are generally parallel, as are the intake valves, but the angles made in the common plane with respect to the reference surface may not be the same for the intake valve set and exhaust valve set. Indeed it is not impossible for the planes of the intake and exhaust valves to be different as well.
Reconditioning operations currently include reboring the valve guides, resurfacing the valve seats, and counterboring for replacement inserts. All these operations require an initial alignment of a tool axis with the common axis of the valve stem and seat for each valve. This has heretofore required meticulous and time consuming setup effort to be repeated 12 or 16 times to align the axes of the reconditioning tools individually at each valve position.